Transmission line having high attenuation for radiant



March 17,1964 D. G. HOLINBECK 3,125,733

E HAVING TTENUATION TRANSMISSION LIN ENERGY INDUCE H A FOR RA NT D HIGHF UENCY CURRE USEF IN DETONATIO IRCUI Filed Nov. 1960 FIG. 2

INVENTOR. DALE G. HOLINBECK ATTORNEY United States Patent TRANSMISSIONLINE HAVING HIGH ATTENUA- This invention relates to electricaltransmission lines, and more particularly relates to transmission lineswherein high frequency electrical energy is attenuated and lowerfrequency energy is transmitted with minimum power attenuation. Thecharacteristic feature of the embodiments of this invention is theprovision of two conductors, at least one of which is helically wound toprovide a high inductive reactance in the circuit and which is separatedfrom the other conductor by a resistive material, which is preferably,of high magnetic permeability.

It is desirable to provide electrical transmission lines forlow-frequency energy that strongly attenuate electromagnetic energy ofhigh frequency that is propagated in the line, for use on aircraftequipped with electrically detonated armament when the aircraft aresituated in the vicinity of high-frequency transmitters. It is possiblethat electrical conductors used for detonating explosive charges mayreceive sufficient electromagnetic radiant energy from radio or radartransmitters to cause sufficient current to be induced to detonatearmament explosives.

The transmission lines of this invention cause highfrequency energy tobe attenuated without causing appreciable power loss at lowerfrequencies. In one embodiment of the invention one conductor ishelically wound around another conductor and is separated therefrom bymeans of electrically resistive material which is preferablycharacterized by high magnetic permeability. In another embodiment ofthe invention two helical conductors are separated by means of beads ofsimilar material.

It is an object of this invention to provide electrical transmissionlines which pass low-frequency energy without appreciable powerattenuation and which attenuate high-frequency energy.

It is another object of this invention to provide a simply constructedtransmission line which attenuates high-frequency electrical energy.

Other objects will become apparent from the drawings and from thefollowing detailed description in which it is intended to illustrate theapplicability of the invention without thereby limiting its scope toless than that of all equivalents which will be apparent to one skilledin the art. In the drawings like reference numerals refer to like partsand:

FIGURE 1 is an elevation of one embodiment of a transmission line ofthis invention which causes highfrequency energy to be attenuated;

FIGURE 2 is an elevation of another embodiment of a transmission line ofthis invention which causes highfrequency current therein to beattenuated.

Present-day military armaments are extensively provided with electricdetonating devices for igniting explosive charges. The circuitry isusually of such character that live armament is fired when a relativelylow-voltage, high-current pulse is produced in the detonator. in manyfield armaments, such as recoilless rifles, and in aircraft armaments itis impractical or undesirable to provide a high-voltage, high-currentpulse for detonating the explosive because the electrical power-packmust be lightweight and easily portable. However, it is necessary toprovide protection against accidental detonation by relativelyhighintensity electro-magnetic energy induced from radio and 3,125,733Patented Mar. 17, 1964 "ice radar equipment. Consequently, conventionalconductors, cables and transmission lines may be exposed to sufiicientelect-ro-magnetic radiation to have induced therein currents of amagnitude suificient to electrically detonate armaments.

The spurious electro-magnetic radiation to which firing circuitconductors are exposed is characteristically highfrequency radiation of=kilocyoles or greater. To protect electrically detonated militaryarmament from accidental firing it is desirable to provide atransmission line which attenuates the high-frequency current, ie 100kc. or greater, which is induced therein, but which enables lowerfrequency current to pass therethrough substantially withoutattenuation, thereby protecting the circuit from accidental activationwhen the armament is in a state of readiness for firing.

If a closely spaced two conductor transmission line has negligibleseries resistance (R), but has appreciable series reactance (X), shuntsusceptance (B) and shunt conductance (G), the expression for theattenuation constant of the line is:

X =21rfL (2) The series reactance is proportional to the seriesinductance (L) and the frequency (f) in the line. A large inductancecharacteristic is conveniently provided by utilizing a helicalconductor. The inductance'of the conductor is proportional to theproduct of the current and the number of turns in the conductor as iswell known. A large series inductance and high-frequency therefor tendsto produce a large attenuation. The bracketed term of Equation 1 mustalso be large if a large attenuation is to be realized, and in general,this implies that between the conductors of a transmission line theremust be a medium having a relatively large conductance. How ever, if amedium which has a large conductance is provided between windings of ahelically Wound conductor, the conductor will be shorted out and theattenuation may not be much greater than that which is obtained from theuse of low-inductance conductors.

In FIGURES 1 and 2 are shown two configurations of conductors thatprovide high 'frequency attenuation in a transmission line. Bothconfigurations utilize solenoidal conductors to provide the necessaryinductance therein. In FIGURE 1 is shown transmission line 10 comprisingconductor 11 embedded in electrically resistive material 12 withconductor 13 wound axially therearound. Material 12 is slotted in aconnoidal configuration between windings of conductor 13 so thatadjacent windings of conductor 13 are not short-circuited by conductivematerial 12. The configuration shown in FIGURE 1 may be easilyfabricated and provides a safe and effective highfrequency attenuatingtransmission line.

Material 12 may be any lossy material, as for example, a material of thefollowing formulation:

Parts Polysulfide resin 100 Carbon black 6O Stearic acid 1 Zinc peroxide4 Calcium hydroxide 1 In preferred embodiments of this inventionnon-conductive or slightly conductive material having high magneticpermeability is incorporated into material 12 to improve the attenuationcharacteristic of the line at high frequencies. Thus, ferrite granulesmay be added although such materials are not essential for operability,to the above material, or alternatively discs of ferrite or othermagnetic non-conductive material may be alternated with discs of theabove material along the length of the lines.

Other materials which may be used include other polymer-ic syntheticresins which are filled with carbon black such as polyethylene,polytetraclrloroethylene, polyvinylidene chloride, and other resinswhich are known as dielectric material for use in electrical equipmentand which may be compounded with carbon black to render them conductiveand dissipative may be used instead of the above compounded composition.Foamed resins may also be used when mixed with carbon black, powderedlead sulfide or other conductive or semi-conductive powdered materials.Sheath 14 of dielectric material such as natural or synthetic rubber,polyvinylchloride or other conventional electrical cable sheathing maybe provided as an outer casing on transmission line If desired, metallicbraid or other operable strengthening or protective material may beplaced on the outside of the cable in operable manner. The slots inmaterial 12 may be filled with a dielectric material such as polymericsynthetic resin or natural or synthetic rubber or other material whichis preferably resilient and flexible.

In FIGURE 2 is shown another embodiment of a transmission line of thisinvention wherein transmission line 15 comprises two solenoidalconductors 1'6 and 17 disposed in side by side relationship andseparated by intermittently spaced beads 18 of electrically resistive,preferably high magnetic permeability material such as syntheticpolymeric resins filled with carbon black and ferrite or the like, orwith carbon black or other resistive material alone in non-preferredembodiments. The conductors 16 and 17 and beads 18 are embedded indielectric material 19 such as natural or synthetic rubber, synthetic(resin or other conventional cable insulating material. If it isdesired, each conductor 16 and 17 may be insulated separately andconnected together by means of beads 18'. While certain modificationsand embodiments of the invention have been described, it is of course tobe understood that there are a great number of variations which willsuggest themselves to anyone familiar with the subject matter thereofand it is to be distinctly understood that this invention should not belimited except by such limitations as are clearly imposed in theappended claims.

I claim:

1. In electrical transmission lines for attenuating high frequencycurrents Without appreciable loss at low frequencies, the combination ofa centrally disposed linear metal conductor, a conductive high frequencydissipative material surrounding said central conductor, ahelicallyformed conductor disposed substantially symmetrically aboutsaid central conductor and extending longitudinally along the lengththereof, said helicallyformed conductor adding inductive reactance tothe circuit and being embedded in said dissipative material, saiddissipative material having a helically configured slot in the outerperiphery thereof extending between successive turns of saidhelically-formed conductor thereby providing a dielectric gap betweenturns of said helically-formed conductor said slot being filled withdielectric material.

2. The article of claim 1 wherein said dissipative material is syntheticresin filled with carbon black.

3. The article of claim 1 wherein said dissipative material comprises aresistive material and a substantially non-conductive, high magneticpermeability material.

4. The article of claim 1 provided with a protective casing therearound.

References Cited in the file of this patent UNITED STATES PATENTS2,228,797 Wasserman Jan. 14, 1941 2,238,915 Peters Apr. 22, 19412,304,210 Scott Dec. 8, 1942 2,322,773 Peters June 29, 1943 2,387,783Tawney' Oct. 30, 1945 2,622,152 Rosch Dec. 16, 1952 2,769,149 Kreer Oct.30, 1956 3,035,237 Shlicke May 15, 1962 3,081,439 Bennett Mar. 12, 1963FOREIGN PATENTS 571,590 Belgium Sept. 29, 1958

1. IN ELECTRICAL TRANSMISSION LINES FOR ATTENDING HIGH FREQUENCYCURRENTS WITHOUT APPRECIABLE LOSS AT LOW FREQUENCIES, THE COMBINATION OFA CENTRALLY DISPOSED LINEAR METAL CONDUCTOR, A CONDUCTIVE HIGH FREQUENCYDISSIPATIVE MATERIAL SURROUNDING SAID CENTRAL CONDUCTOR, AHELICALLYFORMED CONDUCTOR DISPOSED SUBSTANTIALLY SYMMETRICALLY ABOUTSAID CENTRAL CONDUCTOR AND EXTENDING LONGITUDINALLY ALONG THE LENGTHTHEREOF, SAID HELICALLY-FORMED CONDUCTOR ADDING INDUCTIVE REACTANCE TOTHE CIRCUIT AND BEING EMBEDDED IN SAID DISSIPATIVE MATERIAL, SAIDDISSIPATIVE MATERIAL HAVING A HELICALLY CONFIGURED SLOT IN THE OUTERPERIPHERY THEREOF EXTENDING BETWEEN SUCCESSIVE TURNS OF SAIDHELICALLY-FORMED CONDUCTOR THEREBY PROVIDING A DIELECTRIC GAP BETWEENTURNS OF SAID HELICALLY-FORMED CONDUCTOR SAID SLOT BEING FILLED WITHDIELECTRIC MATERIAL.